RUNNING HOT

I put car in shop after it ran hot and battery died. Shop did cooling system pressure test and determined coolant reservoir was cracked. They replaced reservoir and battery and did chemical block test and found gas in coolant so they suspect failed head gasket. Because its a 93 and not worth the cost of head work. I put in bars leak head gasket fix. That fixed rough idle and smoke from exhaust right away and car runs very well now. But still runs hot after 10 or 15 minutes. Would appreciate any advise you can provide thank you. Oz